An integrated circuit (“IC”) is a device that includes many electronic components (e.g., transistors, resistors, diodes, etc.). These components are often interconnected to form multiple circuit components (e.g., gates, cells, memory units, arithmetic units, controllers, decoders, etc.) on the IC. The electronic and circuit components of IC's are jointly referred to below as “components.”
An IC also includes multiple layers of wiring (“wiring layers”) that interconnect its electronic and circuit components. For instance, many IC's are currently fabricated with metal or polysilicon wiring layers (collectively referred to below as “metal layers,” “interconnect layers” or “wiring layers”) that interconnect its electronic and circuit components. One common fabrication model uses five metal layers. In theory, the wiring on the metal layers can be all-angle wiring (i.e., the wiring can be in any arbitrary direction). Such all-angle wiring is commonly referred to as Euclidean wiring. In practice, however, each metal layer typically has a preferred wiring direction, and the preferred direction alternates between successive metal layers. IC designs often penalize non-preferred-direction wiring on a layer.
Many IC's use the Manhattan wiring model, which specifies alternating layers of preferred-direction horizontal and vertical wiring. In this wiring model, the majority of the wires can only make 90° turns. However, occasional diagonal jogs are sometimes allowed on the preferred horizontal and vertical layers.
Design engineers design IC's by transforming circuit description of the IC's into geometric descriptions, called layouts. To create layouts, design engineers typically use electronic design automation (“EDA”) applications. These applications provide sets of computer-based tools for creating, editing, and analyzing IC design layouts.
EDA applications create layouts by using geometric shapes that represent different materials and devices on IC's. For instance, EDA tools commonly use rectangular lines to represent the wire segments that interconnect the IC components. These tools also represent electronic and circuit IC components as geometric objects with varying shapes and sizes.
Also, in this document, the phrase “circuit module” refers to the geometric representation of an electronic or circuit IC component by an EDA application. EDA applications typically illustrate circuit modules with pins on their sides. These pins connect to the interconnect lines.
A net is typically defined as a collection of pins that need to be electrically connected. A list of all or some of the nets in a layout is referred to as a netlist. In other words, a netlist specifies a group of nets, which, in turn, specify the required interconnections between a set of pins. The IC design process entails various operations. Some of the physical-design operations that EDA applications commonly perform to obtain the IC layouts are: (1) circuit partitioning, which partitions a circuit if the circuit is too large for a single chip; (2) floor planning, which finds the alignment and relative orientation of the circuit modules; (3) placement, which determines more precisely the positions of the circuit modules; (4) routing, which completes the interconnects between the circuit modules; and (5) verification, which checks the layout to ensure that it meets design and functional requirements.
Routing is a key operation in the physical design cycle. It is generally divided into two phases: global routing and detailed routing. For each net, global routing generates a “loose” route for the interconnect lines that are to connect the pins of the net. After global routes have been created, the detailed routing creates specific individual routing paths for each net.
While some commercial routers today might allow an occasional diagonal jog, these routers do not typically explore diagonal routing paths consistently when they are specifying the routing geometries of the interconnect lines. This, in turn, increases the total wircength (i.e., total length of interconnect lines) needed to connect the nets in the layout.
In addition, routers today are mostly gridded. The manufacturing processes for designing IC's specify a manufacturing grid that specifies manufacturable resolution. The boundary of all circuit elements is defined by the straight-line connections between adjacent manufacturing points. Gridded routers typically define arbitrary grids of intersecting lines to specify the available locations for routing interconnects. These arbitrary grids are often much coarser than the manufacturing grids (e.g., they are typically line-to-via spacing). Consequently, they arbitrarily limit the locations of interconnect lines and impose arbitrary spacing between the items in the layout. These arbitrary limits increase the size and efficiency of a design. The routing grids also discourage using arbitrary widths or spacing for interconnect lines. Furthermore, existing routers primarily utilize preferred-direction wiring to route their designs. Many IC layouts are designed by penalizing the use of interconnect lines in each particular layer when the interconnect lines are not in the preferred wiring direction of the particular layer. Such preferred-direction wiring leads to IC layouts and IC's that have most of their interconnect lines and wiring on each of their metal layers traverse in the same direction. Such IC layouts and IC's do not efficiently use the available spacing on the interconnect layers, and this adversely affects the size and efficiency of the layouts and the IC's.